Fluoride Ions Post-Treatment Regulates Interfacial Charge Separation and Transport to Promote Solar Water Splitting of Bismuth Vanadate.

Herein, we propose a simple and effective fluoride (F-) ions post-treatment method to improve the solar water splitting performance of BVO. The surface modification of BVO with functional F- ions not only facilitates the transfer and separation efficiency of carriers at the electrode/electrolyte interface but also promotes the adsorption and activation of water, resulting in a photocurrent of 3.2 mA/cm2 at a bias voltage of 1.2 VRHE. Furthermore, the transfer and separation of carriers in the bulk and on the surface are further regulated by the oxygen vacancies induced by F- ions, thereby enhancing the PEC water splitting performance of BVO. Notably, the experimental findings demonstrate that the inclusion of F- ions in the KBi electrolyte enhances the photo-charging process of BVO. Specifically, at a bias voltage of 0.6 VRHE, the BVO-0.12F sample exhibits a stable photocurrent of 1.2 mA/cm2, which is twice as high as that of the initial BVO sample. Remarkably, our study unveils that the addition of F- ions into the KBi electrolyte solution plays a pivotal role in facilitating the separation of charge carriers and promoting interfacial charge transport. Consequently, this further leads to a substantial enhancement in the solar water splitting performance for BVO-0.12F photoanode.

Pseudocapacitance-Dominated MnNb2 O6 -C Nanofiber Anode for Li-Ion Batteries.

MnNb2 O6 anode has attracted much attention owing to its unique properties for holding Li ions. Unluckily, its application as a Li-ion battery anode is restricted by low capacity because of the inferior electronic conductivity and limited electron transfer. Previous studies suggest that structure and component optimization could improve its reversible capacity. This improvement is always companied by capacity increments, however, the reasons have rarely been identified. Herein, MnNb2 O6 -C nanofibers (NFs) with MnNb2 O6 nanoparticles (~15 nm) confined in carbon NFs, and the counterpart MnNb2 O6 NFs consisting of larger nanoparticles (40-100 nm) are prepared by electrospinning for clarifying this phenomenon. The electrochemical evaluations indicate that the capacity achieved by the MnNb2 O6 NF electrode presents an activation process and a degradation in subsequence. Meanwhile, the MnNb2 O6 -C NF electrode delivers high reversible capacity and ultra-stable cycling performance. Further analysis based on electrochemical behaviors and microstructure changes reveals that the partial structure rearrangement should be in charge of the capacity increment, mainly including pseudocapacitance increment. This work suggests that diminishing the dimensions of MnNb2 O6 nanoparticles and further confining them in a matrix could increase the pseudocapacitance-dominated capacity, providing a novel way to improve the reversible capacity of MnNb2 O6 and other intercalation reaction anodes.

Kinetically well-matched porous framework dual carbon electrodes for high-performance sodium-ion hybrid capacitors.

Sodium-ion hybrid capacitors (SIHCs) have attracted extensive interest due to their applications in sodium-ion batteries and capacitors, which have been considered expectable candidates for large-scale energy storage systems. The crucial issues for achieving high-performance SIHCs are the reaction kinetics imbalances between the slow Faradic battery-type anodes and fast non-Faradaic capacitive cathodes. Herein, we propose a simple self-template strategy to prepare kinetically well-matched porous framework dual-carbon electrodes for high-performance SIHCs, which stem from the single precursor, sodium ascorbate. The porous framework carbon (PFC) is obtained by direct calcination of sodium ascorbate followed by a washing process. The sodium-ion half cells with PFC anodes exhibit high reversible capacity and fast electrochemical kinetics for sodium storage. Moreover, the as-obtained PFC can be further converted to porous framework activated carbon (PFAC) with rich porosity and a high specific surface area, which displays high capacitive properties. By using kinetically well-matched battery-type PFC anodes and capacitive PFAC cathodes, dual-carbon SIHCs are successfully assembled, which can work well in 0-4 V. The optimal PFC//PFAC SIHC exhibits high energy density (101.6 Wh kg-1 at 200 W kg-1), power density (20 kW kg-1 at 51.1 Wh kg-1), and cyclic performance (71.8 % capacitance attenuation over 10,000 cycles).

Self-induced matrix with Li-ion storage activity in ultrathin CuMnO2 nanosheets electrode.

Conversion anode materials such as Mn3O4 draw much attention due to their considerable theoretical capacity for lithium-ion batteries (LIBs). However, poor conductivity, slow solid-state Li-ion diffusion, and huge volume expansion of the active materials during charge/discharge lead to unsatisfied electrochemical performance. Despite several strategies like nanocrystallization, fabricating hierarchical nanostructures, and introducing a matrix are valid to address these crucial issues, the achieved electrochemical performance still needs to be further enhanced. What is worse, the matrix with less or no Li-ion storage activity may lower the achieved capacity of the electrodes. Herein, ultra-thin CuMnO2 nanosheets with the thickness of 5-8 nm were evaluated for LIBs. The ultra-thin sheet-like nanostructure offers sufficient contact areas with electrolyte and shortens the Li-ion diffusion distance. Moreover, the in-situ generated Mn and Cu along with their oxides could play the role of matrix and conductive agent in turn at different stages, relieving the stress brought by volume expansion. Therefore, the as-prepared ultra-thin CuMnO2 nanosheets electrode displays a remarkable reversible capacity, long cycling stability, and outstanding rate capability (a reversible capacity of 1160.5 mAh g-1 at 0.1A g-1 was retained after 100 cycles with a capacity retention of 95.1 %, and 717.8 mAh g-1 at 2.0 A g-1 after 400 cycles).

Structure engineering of silicon nanoparticles with dual signals for hydrogen peroxide detection.

Fluorescent silicon nanoparticles (SiNPs) were synthesized by a one-step, simple, and green method with 3-Aminopropyltriethoxysilane (APTES) and ascorbic acid (AA) as reaction agents. Subsequently, the SiNPs and AgNPs nanocomplex (SiNPs@AgNPs) was constructed as the probe for hydrogen peroxide (H2O2) detection. The fluorescence of SiNPs was quenched due to the surface plasmonic-enhanced energy transfer between SiNPs and AgNPs. Meanwhile, the color tends to be yellow due to the existence of AgNPs. As the AgNPs were etched by H2O2, the fluorescence recovers and color fadings. Based on the well-designed structure, the "off-on" fluorescence sensing and "on-off" color sensing platforms for H2O2 were fabricated. The as-synthesized materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Fluorescence and UV-vis absorption spectra were used to evaluate the optical performance. The fabricated sensor exhibited a linear range of 1.0-100.0 µM, with a limit of detection of 0.36 µM for the fluorescence sensing of H2O2. Additionally, a linear range of 1.0-50.0 µM and a limit of detection of 0.45 µM were displayed for the detection of H2O2 by colorimetric assay. The feasibility in complex medium of the fabricated fluorescent and colorimetric dual-signal sensor was evaluated by the detection of H2O2 in phosphate buffer saline (PBS) and lake water samples.

Heterostructure engineering of ultrathin SnS2/Ti3C2Tx nanosheets for high-performance potassium-ion batteries.

Layered metal sulfides are considered as promising candidates for potassium ion batteries (KIBs) owing to the unique interlayer passages for ion diffusion. However, the insufficient electronic conductivity, inevitable volume expansion, and sulfur loss hinder the promotion of K-ion storage performance. Herein, few-layered Ti3C2Tx nanosheets were selected as the multi-functional substrate for cooperating few-layered SnS2 nanosheets, constructing SnS2/Ti3C2Tx hetero-structural nanosheets (HNs) with the thickness as thin as about 5 nm. In this configuration, the formed Ti-S bonds provide robust interaction between SnS2 and Ti3C2Tx nanosheets, which hinders the agglomeration of SnS2 and the restack of Ti3C2Tx, endowing the hybrid material with robust nanostructure. Thus, the shortcomings of the SnS2 anode are muchly relieved. In this way, the as-prepared SnS2/Ti3C2Tx HNs electrode delivers reversible capacities of 462.1 mAh g-1 at 0.1 A g-1 and 166.1 mAh g-1 at 2.0 A g-1, respectively, and a capacity of 85.5 mAh g-1 is remained even after 460 cycles at 2.0 A g-1. These results are superior to those of the counterpart electrode, confirming aggressive promotion of K-ion storage performance of SnS2 anode brought by the cooperation of Ti3C2Tx, and presenting a reliable strategy to improve the electrochemical performance of sulfide anodes.

F- regulate the preparation of polyhedral BiVO4 enclosed by High-Index facet and enhance its photocatalytic activity.

The selective exposure of high-index facets at the surface of nanocrystals is an important and challenging research topic. Herein, polyhedral bismuth vanadate (BiVO4) crystals predominantly surrounded by {2 1 3} and {1 2 1} high-index facets were fabricated through the engineering of high-index surfaces by fluorinion (F-) mediated hydrothermal process. The as-prepared BiVO4-0.2F (the feeding amount of NaF was 0.2 g) catalyst exhibited high apparent quantum efficiency of 17.7% under 420 nm light irradiation and 9.3 fold enhancement of O2 evolution relative to its low-index counterparts. Moreover, the growth of high-index facets results in significant enhancement of hydroxyl radical (•OH) production, photocatalytic degradation of Rhodamine B (RhB) and photoelectrochemical (PEC) properties by the BiVO4 polyhedron, relative to its low-index counterparts. The enhanced photoreactivity is the result of the synergistic effect of F- on the surface of the BiVO4 crystals and exposed high-index facets. For one thing, F- on the surface of the BiVO4 facilitate the separation and transport of photo-induced charge carriers. For another, the exposed high-index facets on polyhedral BiVO4 provided much more reactive sites for photocatalytic reactions. Hopefully, this F- mediated method will be a useful guideline for designing and synthesizing novel high-index faceted micro-/nanostructures for overcoming the practical energy and environment problems.

A TiSe2 -Graphite Dual Ion Battery: Fast Na-Ion Insertion and Excellent Stability.

The sodium dual ion battery (Na-DIB) technology is proposed as highly promising alternative over lithium-ion batteries for the stationary electrochemical energy-storage devices. However, the sluggish reaction kinetics of anode materials seriously impedes their practical implementation. Herein, a Na-DIB based on TiSe2 -graphite is reported. The high diffusion coefficient of Na-ions (3.21×10-11 -1.20×10-9  cm2 s-1 ) and the very low Na-ion diffusion barrier (0.50 eV) lead to very fast electrode kinetics, alike in conventional surface capacitive storage systems. In-situ investigations reveal that the fast Na-ion diffusion involves four insertion stage compositions. A prototype cell shows a reversible capacity of 81.8 mAh g-1 at current density of 100 mA g-1 , excellent stability with 83.52 % capacity retention over 200 cycles and excellent rate performance, suggesting its potential for next-generation large scale high-performance stationary energy storage systems.

Stimulating the Reversibility of Sb2 S3 Anode for High-Performance Potassium-Ion Batteries.

Conversion-alloy sulfide materials for potassium-ion batteries (KIBs) have attracted considerable attention because of their high capacities and suitable working potentials. However, the sluggish kinetics and sulfur loss result in their rapid capacity degeneration as well as inferior rate capability. Herein, a strategy that uses the confinement and catalyzed effect of Nb2 O5 layers to restrict the sulfur species and facilitate them to form sulfides reversibly is proposed. Taking Sb2 S3 anode as an example, Sb2 S3 and Nb2 O5 are dispersed in the core and shell layers of carbon nanofibers (C NFs), respectively, constructing core@shell structure Sb2 S3 -C@Nb2 O5 -C NFs. Benefiting from the bi-functional Nb2 O5 layers, the electrochemical reversibility of Sb2 S3 is stimulated. As a result, the Sb2 S3 -C@Nb2 O5 -C NFs electrode delivers the rapidest K-ion diffusion coefficient, longest cycling stability, and most excellent rate capability among the controlled electrodes (347.5 mAh g-1 is kept at 0.1 A g-1 after 100 cycles, and a negligible capacity degradation (0.03% per cycle) at 2.0 A g-1 for 2200 cycles is delivered). The enhanced K-ion storage properties are also found in SnS2 -C@Nb2 O5 -C NFs electrode. Encouraged by the stimulated reversibility of Sb2 S3 and SnS2 anodes, other sulfides with high electrochemical performance also could be developed for KIBs.

Li-N2 Batteries: A Reversible Energy Storage System?

Tremendous energy consumption is required for traditional artificial N2 fixation, leading to additional environmental pollution. Recently, new Li-N2 batteries have inextricably integrated energy storage with N2 fixation. In this work, graphene is introduced into Li-N2 batteries and enhances the cycling stability. However, the instability and hygroscopicity of the discharge product Li3 N lead to a rechargeable but irreversible system. Moreover, strong nonpolar N≡N covalent triple bonds with high ionization energies also cause low efficiency and irreversibility of Li-N2 batteries. In contrast, the modification with in situ generated Li3 N and LiOH restrained the loss and volume change of Li metal anodes during stripping and plating, thereby promoting the rechargeability of the Li-N2 batteries. The mechanistic study here will assist in the design of more stable Li-N2 batteries and create more versatile methods for N2 fixation.

CuO Nanoplates for High-Performance Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) are promising alternatives to lithium-ion batteries because of the abundance and low cost of K. However, an important challenge faced by KIBs is the search for high-capacity materials that can hold large-diameter K ions. Herein, copper oxide (CuO) nanoplates are synthesized as high-performance anode materials for KIBs. CuO nanoplates with a thickness of ≈20 nm afford a large electrode-electrolyte contact interface and short K+ ion diffusion distance. As a consequence, a reversible capacity of 342.5 mAh g-1 is delivered by the as-prepared CuO nanoplate electrode at 0.2 A g-1 . Even after 100 cycles at a high current density of 1.0 A g-1 , the capacity of the electrode remains over 206 mAh g-1 , which is among the best values for KIB anodes reported in the literature. Moreover, a conversion reaction occurs at the CuO anode. Cu nanoparticles form during the first potassiation process and reoxidize to Cu2 O during the depotassiation process. Thereafter, the conversion reaction proceeds between the as-formed Cu2 O and Cu, yielding a reversible theoretical capacity of 374 mAh g-1 . Considering their low cost, easy preparation, and environmental benignity, CuO nanoplates are promising KIB anode materials.

Controllable N-Doped CuCo2 O4 @C Film as a Self-Supported Anode for Ultrastable Sodium-Ion Batteries.

Rational synthesis of flexible electrodes is crucial to rapid growth of functional materials for energy-storage systems. Herein, a controllable fabrication is reported for the self-supported structure of CuCo2 O4 nanodots (≈3 nm) delicately inserted into N-doped carbon nanofibers (named as 3-CCO@C); this composite is first used as binder-free anode for sodium-ion batteries (SIBs). Benefiting from the synergetic effect of ultrasmall CuCo2 O4 nanoparticles and a tailored N-doped carbon matrix, the 3-CCO@C composite exhibits high cycling stability (capacity of 314 mA h g-1 at 1000 mA g-1 after 1000 cycles) and high rate capability (296 mA h g-1 , even at 5000 mA g-1 ). Significantly, the Na storage mechanism is systematically explored, demonstrating that the irreversible reaction of CuCo2 O4 , which decomposes to Cu and Co, happens in the first discharge process, and then a reversible reaction between metallic Cu/Co and CuO/Co3 O4 occurrs during the following cycles. This result is conducive to a mechanistic study of highly promising bimetallic-oxide anodes for rechargeable SIBs.

FeMnO3: a high-performance Li-ion battery anode material.

In this communication, FeMnO3 particles were prepared and evaluated as an anode material for Li ion batteries. This electrode shows high capacity, excellent rate capability, and good cycling stability (984 mA h g-1 at 1.0 A g-1 after 500 cycles). Moreover, the Li storage mechanism is studied.

Reconstruction of Mini-Hollow Polyhedron Mn2O3 Derived from MOFs as a High-Performance Lithium Anode Material.

A mini-hollow polyhedron Mn2O3is used as the anode material for lithium-ion batteries. Benefiting from the small interior cavity and intrinsic nanosize effect, a stable reconstructed hierarchical nanostructure is formed. It has excellent energy storage properties, exhibiting a capacity of 760 mAh g-1 at 2 A g-1 after 1000 cycles. This finding offers a new perspective for the design of electrodes with large energy storage.

Na2 Ti6 O13 Nanorods with Dominant Large Interlayer Spacing Exposed Facet for High-Performance Na-Ion Batteries.

As the delegate of tunnel structure sodium titanates, Na2 Ti6 O13 nanorods with dominant large interlayer spacing exposed facet are prepared. The exposed large interlayers provide facile channels for Na(+) insertion and extraction when this material is used as anode for Na-ion batteries (NIBs). After an activation process, this NIB anode achieves a high specific capacity (a capacity of 172 mAh g(-1) at 0.1 A g(-1) ) and outstanding cycling stability (a capacity of 109 mAh g(-1) after 2800 cycles at 1 A g(-1) ), showing its promising application on large-scale energy storage systems. Furthermore, the electrochemical and structural characterization reveals that the expanded interlayer spacings should be in charge of the activation process, including the enhanced kinetics, the lowered apparent activation energy, and the increased capacity.

Ultrasmall TiO2 Nanoparticles in Situ Growth on Graphene Hybrid as Superior Anode Material for Sodium/Lithium Ion Batteries.

To inhibit the aggregation of TiO2 nanoparticles and to improve the electrochemical kinetics of TiO2 electrode, a hybrid material of ultrasmall TiO2 nanoparticles in situ grown on rGO nanosheets was obtained by ultraphonic and reflux methods. The size of the TiO2 particles was controlled about 10 nm, and these particles were evenly distributed across the rGO nanosheets. When used for the anode of a sodium ion battery, the electrochemical performance of this hybrid TiO2@rGO was much improved. A capacity of 186.6 mAh g(-1) was obtained after 100 cycles at 0.1 A g(-1), and 112.2 mAh g(-1) could be maintained at 1.0 A g(-1), showing a high capacity and good rate capability. On the basis of the analysis of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the achieved excellent electrochemical performance was mainly attributed to the synergetic effect of well-dispersed ultrasmall TiO2 nanoparticles and conductive graphene network and the improved electrochemical kinetics. The superior electrochemical performance of this hybrid material on lithium storage further confirmed the positive effect of rGO.

Exfoliated-SnS2 restacked on graphene as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries.

Designed as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, exfoliated-SnS2 restacked on graphene is prepared by the hydrolysis of lithiated SnS2 followed by a facile hydrothermal method. Structural and morphological characterizations demonstrate that ultrasmall SnS2 nanoplates (with a typical size of 20-50 nm) composed of 2-5 layers are homogeneously decorated on the surface of graphene, while the hybrid structure self-assembles into a three-dimensional (3D) network architecture. The obtained SnS2/graphene nanocomposite delivers a remarkable capacity as high as 650 mA h g(-1) at a current density of 200 mA g(-1). More impressively, the capacity can reach 326 mA h g(-1) even at 4000 mA g(-1) and remains stable at ∼610 mA h g(-1) without fading up to 300 cycles when the rate is brought back to 200 mA g(-1). The excellent electrochemical performance is attributed to the synergetic effects between the ultrasmall SnS2 and the highly conductive graphene network. The unique structure can simultaneously facilitate Na(+) ion diffusion, provide more reaction sites, and suppress aggregation and volume fluctuation of the active materials during prolonged cycling.

Synthesis of rGO-supported layered MoS2 for high-performance rechargeable Mg batteries.

Distinctive rGO-supported MoS2 hybrids have been fabricated via a hydrothermal method followed by a heat treatment. Characterizations demonstrate that layered MoS2 and graphene nanosheets in the hybrids interlace with each other to form novel sandwich-structured microspheres, which exhibit preferable electrochemical performance in rechargeable Mg batteries.

Polyol-mediated synthesis of mesoporous α-Ni(OH)2 with enhanced supercapacitance.

Flower-like α-Ni(OH)2 microspheres composed of nanowires are prepared by a solvothermal method using triethylene glycol and water as the mixed solvent. The formation of this unique structure is attributed to the synergetic effect of dissolution-recrystallization procedure, Ostwald ripening, and aggregative lateral attachment. Experimental results indicate that the dielectric constant, viscosity, and the chain lengths of the alcohols in the solvent may greatly affect the morphology and size of the as-obtained α-Ni(OH)2 samples. Because of the high Brunauer, Emmett, and Teller (BET) nitrogen sorption surface area of 318 m(2) g(-1) and large pore volume, this sample displays a maximum discharge specific capacity of 1788.9 F g(-1) at a discharge current density of 0.5 A g(-1). Besides, rate performance of this sample is also excellent, indicating that this sample is promising in electrochemical supercapacitors.